The invention relates to a chip resistor comprising a cuboid resistor body of ceramic material and solderable, metal, current-supply strips at a first pair of opposite side faces of the resistor body.
The invention also relates to a method of manufacturing such a chip resistor.
The invention can particularly suitably be applied to reistors having no lead wires, a semiconductive ceramic material being used as a resistance material, in particular materials having a negative (NTC) or a high positive (PTC) temperature coefficient of electrical resistance.
U.S. Pat. No. 3,027,529 describes a PTC resistor, in which a resistor body in the form of a cylinder or a disc is used. The electric connections consist of metal caps which are fitted around the ends of the cylinder, or of lead wires which are soldered to the flat sides of the disc.
In the manufacture of electric components having no lead wires, the dimensions of which should be as small as possible, and which should be manufactured at low costs, the application of caps is undesired in many cases. According to an alternative method, contact faces for the supply of electric current are manufactured by means of sputtering, metal spraying or vapour deposition, but it is not easy to manufacture contact faces which extend around the edges of the component by such methods.
Components having no lead wires, which are preferably cuboid, should at each end be provided with terminals on three faces owing to the various soldering techniques used for mounting on a printed circuit board. In the case of wave-soldering, a component is temporarily fixed to a printed circuit board by means of an adhesive, after which a solder wave is led over the surface of the board. This technique requires the presence of terminals at the side faces of the electric component. In a vapour soldering process, drops of a solder paste are placed on the printed circuit board, after which the electric components are provided and the assembly is heated in a vapour, the solder paste being converted into a conductive contact material. This technique requires the presence of terminals on the lower side of the electric component which lies against the printed circuit board. For reasons of symmetry there is preferably also a terminal on the upper side, so as to render an additional check superfluous when the electric component is mounted on the printed circuit board.
Electric contact faces extending around the edges of a component can be manufactured in known manner in an immersion process, for example by means of an electroless metallizing bath followed by electrodeposition, or by means of a metal paste. In an emerging process which is applied to a resistor body which consists completely of resistance material, there is the problem that the immersion depth, and, hence, the resistance value is hard to control accurately. Unlike a thin-film resistor, the proper resistance value cannot simply be obtained by trimming, for example, using a laser. On the other hand, the use of resistors which consist predominantly of resistance material is important, for example, for the manufacture of accurate resistors having a low resistance value, for applications involving a high electric power rating and for the manufacture of NTC and PTC resistors from semiconductive ceramic material.